Scientific Background | Conventional protein labelling chemistry targets lysine or cysteine side chains, which are usually present in multiple copies, so the product is a mixture differing in how many labels each molecule carries and where. Sortase A avoids this. The bacterial transpeptidase recognises the LPXTG motif, cleaves after the threonine and joins the remainder to an incoming glycine nucleophile, installing exactly one label at exactly one position. This product supplies that recognition motif carrying IRDye 800CW. Emission in the 800 nm window is the operative feature: tissue absorbs and scatters far less at these wavelengths than in the visible range and autofluorescence is markedly lower, so signal survives depth that would defeat a visible fluorophore. For whole-organ imaging, thick sections and live animal work, that is usually the deciding consideration. The same chemistry underpins intercellular labelling methods, in which sortase displayed on one cell transfers its substrate onto any cell it touches, leaving a lasting record of the encounter that can be read out later. Approaches of this kind have been used to monitor T cell and dendritic cell interactions in vivo and, more recently, to record immune cell interactions generally. |
References | 1. Pasqual G, Chudnovskiy A, Tas JMJ, et al. Monitoring T cell-dendritic cell interactions in vivo by intercellular enzymatic labelling. Nature (2018) 553:496. doi:10.1038/nature25442 2. Nakandakari-Higa S, Walker S, Canesso MCC, et al. Universal recording of immune cell interactions in vivo. Nature (2024) 627:399. doi:10.1038/s41586-024-07134-4 |
